1. Field of the Invention
The present invention relates to polypropylene resin compositions having excellent crystallizability, high transmittance, high clarity, low haze, and improved thermal stability. More particularly, the present invention relates to a polypropylene resin composition comprising p-urea phenyl derivatives to reduce haze.
2. Description of Related Art
It is known that crystalline polypropylene may occur in α, β, γ, and δ crystal forms as well as in the smectic crystal form which is formed on quenching of melted polypropylene. The β-crystal form differs from the form found in the conventional natural pellet in that it is lower in melting point and in density and exhibits differences in the mode of crystallization and fracture.
For the production of crystalline polypropylene containing the β-form, processes comprising blending with a small amount of a nucleating agent (hereinafter referred to as “β-nucleating agent”) are known.
Typical nucleating agents known in the art include minerals, such as chalk, clay, kaolin, talc, silicates, and the like. Organic nucleating agents, such as salts of aliphatic or aromatic carboxylic acids, aromatic salts, metallic salts of aromatic phosphorus compounds, quinaridones, aromatic amides, and polymers having melting points are more efficient.
U.S. Pat. No. 3,852,237 discloses a combination of agents, such as sodium benzoate with phthalocyanine, that is said to improve the clarity of nucleated polyolefin, such as polypropylene, in molded objects. It is also disclose that the haze experienced with a single nucleating agent is reduced.
U.S. Pat. No. 4,016,118 discloses a polyolefin plastic composition said to have improved transparency and reduced molding shrinkage, which consists essentially of at least one polymer or copolymer of an aliphatic monoolefin and dibenzylidene sorbitol, the proportion of the dibenzylidene sorbitol being 0.1 to 0.7% by weight based on the total weight of the composition.
U.S. Pat. No. 4,338,228 discloses a polyolefin composition comprising a modified polyolefin obtained by adding an unsaturated carboxylic acid or an anhydride thereof to a polyolefin or mixtures of said modified polyolefin and an unmodified polyolefin, an inorganic filler, one or more nucleating agents or a combination thereof with one or more heat deterioration inhibitors. The polyolefin composition is said to evidence reduced deterioration by heat or reduction of its mechanical strength during a molding operation.
U.S. Pat. No. 4,371,645 discloses a polyolefin plastic composition having improved transparency which comprises a polymer selected from aliphatic polyolefins and copolymers containing at least one aliphatic olefin and one or more ethylenically unsaturated aliphatic comonomers, and a di-acetal of sorbitol of a specified structure in an amount sufficient to improve transparency.
U.S. Pat. No. 4,562,265 discloses a method for producing a di-acetal of sorbitol and an aromatic aldehyde wherein an aqueous solution containing a catalytic amount of a mineral acid and sorbitol is formed. Thereafter, an effective amount of an aromatic aldehyde such as benzaldehyde is incrementally admixed into the homogeneous aqueous admixture containing the sorbitol at a rate sufficient to allow a substantially spontaneous reaction to occur between the D-sorbitol and aromatic aldehyde; thus, forming an aqueous slurry containing crude di-acetal, e.g., dibenzylidene sorbitol. The amount of aromatic aldehyde employed is that amount sufficient to provide a molar ratio of D-sorbitol to aromatic aldehyde of from about 1:0.75 to about 1:1.75. Thereafter, the aqueous slurry is neutralized, and crude di-acetal is removed from the liquid phase and washed with water to remove mono-acetal impurities, e.g., monobenzylidene sorbitol. The washed di-acetal may then be dried to provide dried di-acetal, and the dried di-acetal may be further purified by washing with a relatively non-polar solvent
U.S. Pat. No. 4,585,817 discloses the preparation of linear low density polyethylene and copolymers of ethylene with at least one alpha-olefin containing 3-8 carbon atoms having increased temperature of crystallization and rate of crystallization by incorporating a proportion of highly isotactic polypropylene therein with the nucleating compound dibenzylidene sorbitol or phenyl phosphate compound.
U.S. Pat. No. 4,694,064 discloses the preparation of rod-shaped dendrimers having a plurality of dendritic branches emanating from an essentially linear core by first reacting a linear polyfunctional core compound such as a polyethyleneimine with a first dendritic branching reactant such as an ester of an unsaturated carboxylic acid, e.g., methyl acrylate, and then successively reacting the resulting product with a second dendritic branching reactant such as ethylenediamine and then with the first or another dendritic branching reactant. The rod-shaped dendrimers are said to be useful in the production of molecular composites and as crystallinity modifiers for polymeric materials.
U.S. Pat. No. 4,749,736 discloses a crystalline polyamide corporation having dispersed therein a nucleating agent composed of one or more finely divided inorganic materials, one or more fatty acid amides and one or more low molecular weight polymers selected from the group consisting of polyolefins, polyoxides and polsulfides.
U.S. Pat. No. 5,049,605 discloses bis(3,4-dialkylbenzylidene) sorbitol acetals for the formula:
in which R1 and R2 are independently selected from lower alkyl groups containing 1-4 carbon atoms, or together form a carbocyclic ring containing up to 5 carbon atoms.
U.S. Pat. No. 5,137,973 discloses a crystalline polyolefin composition having dispersed therein a nucleating agent composed of one or more polyesters.
U.S. Pat. No. 5,198,484 discloses a process for incorporating a clarifying agent into a semi-crystalline resin whereby a clarifying agent selected from compounds having the formula:
wherein p is 0 or 1, m and n are independently 0-3, and R is, at each occurrence, independently selected from C1-8 alkyl, C1-4 alkoxy, hydroxy, halogen, C1-6 alkylthio, C1-6 alkylsulfoxy and a 4 or 5 membered alkyl group forming a carbocyclic ring with adjacent carbon atoms of the unsaturated parent ring, and wherein the clarifying agent is in the form of a powder characterized by a d97 of 30 microns or less, and a mean particle size of 15 microns or less, is blended with the polyolefin resin, at a temperature above 170° C. until the clarifying agent is dissolved in the molten resin.
U.S. Pat. No. 5,216,051 discloses tri-acetal polyol compounds and a crystalline polyolefin composition having dispersed therein a nucleating agent composed of one or more of said polyol acetals.
U.S. Pat. No. 5,278,216 discloses a syndiotactic polypropylene resin composition comprising a polypropylene having a substantially syndiotactic structure and a nucleating agent. The syndiotactic polypropylene may be a homopolymer of the propylene, a copolymer of the propylene and a smaller amount of another olefin or a mixture of the above-mentioned (co)polymer and an isotactic polypropylene. The resin composition preferably has a higher crystallization temperature than a polypropylene containing no nucleating agent by 5° C. or more, as measurement is made by a differential scanning thermal analysis.
U.S. Pat. No. 5,574,174 discloses certain 1,3-2,4-di(substituted arylidene)-and 1,3-2,4-di(substituted heteroarylidene)-D-sorbitols that are said to be useful as clarifying and nucleating additives for crystalline and semi-crystalline polyolefin compositions. Also disclosed are such poly(C1-C8 alpha olefin) compositions containing them.
U.S. Pat. No. 6,235,823 discloses a crystalline polypropylene resin composition comprising a crystalline polyproplylene resin and a β-nucleating agent, and a method of increasing the proportion of β-form crystals in a crystalline polypropylene resin molding comprising molding the composition, the β-nucleating agent being a diamide compound.
U.S. Published Patent Application Publication No. 2001/0016259 discloses a sizing composition for glass fibers used to reinforce thermoplastic resins, such as polyolefins, and particularly, polypropylene. The composites produced with the fiber strands coated with such sizing compositions have improved fiber adhesion and retention of fiber length. In addition, a method for improving tensile creep and tensile fatigue in polypropylene composites reinforced with glass fibers is provided.
U.S. Published Patent Application Publication No. 2005/0203226 discloses a composition containing (1) a crystalline polypropylene resin and (2) one or more .beta.-nucleating agents of the formula (I),
wherein R1, R2 and R3, independently of one another, are C1-C20 alkyl, C2-C20 alkyl substituted by C1-C10 alkylamino, di(C1-C10 alkyl)amino, C1-C10 alkyloxy or hydroxy; C3-C20 alkenyl, C5-C12 cycloalkyl, C5-C12 cycloalkyl substituted by 1, 2 or 3 C1-C10 alkyl; cyclohexylmethyl; cyclohexylmethyl substituted by 1, 2 or 3 C1-C10 alkyl; C5-C9 cycloalkenyl, C5-C9 cycloalkenyl substituted by 1, 2 or 3 C1-C10 alkyl; phenyl substituted by 1, 2 or 3 radicals selected from the group consisting of C1-C10-alkyl, C1-C10alkyloxy, hydroxy, halogen, trihalogenmethyl, trihalogenmethoxy, benzoyl, phenylamino, acylamino and phenylazo; C7-C9 phenylalkyl, C7-C9 phenylalkyl which is substituted on the phenyl by 1, 2 or 3 radicals selected from the group consisting of C1-C10 alkyl, C1-C10 alkoxy and hydroxy; naphthyl, naphthyl substituted by C1C10 alkyl, adamantyl, or a 5 to 6 membered heterocyclic group; characterized in that the polypropylene resin has a content of β-form crystals of at least 10% calculated by means of the following equation β-form crystal content (%)=100×P⊕1,/(Pa1+Pa2+Pa3+Pβ1) where Pa1 to Pa3 are respective peak heights (maxima) of the a-form and Pβ1 is a peak height (maximum) of the β-form determined by wide angle X-ray scattering.
WO 95/13317 discloses films formed from blends of high impact LLDPE and sorbitol derivatives that are said to exhibit excellent optical properties, particularly haze properties.
WO 02/46300 discloses a polypropylene composition containing the components: a) a crystallizable polypropylene homopolymer, random copolymer, alternating or segmented block copolymer or a blend of polypropylene with another synthetic polymer, and b) 0.001 to 5% relative to the weight of component b), of a specific trimesic acid derivative.
WO 03/102069 discloses aromatic triamide nucleating agents.
WO 2004/072168 discloses a composition containing a) a natural or synthetic polymer and b) one or more compounds of one of the following formulae wherein R1, R2, and R3 or Y1, Y2, and Y3, or Z1, Z2, and Z3 are chosen from an extensive listing of moieties, e.g., branched C3-C20 alkyl.


WO 2005/040263 discloses a glass fiber-reinforced molding composition composed of an olefin polymer, in particular a propylene polymer. The molding composition comprises and olefin polymer which contains 5-50% by weight of glass fibers which are bonded to the olefin polymer by means of a compatibilizer, and from 10−4 to 1% by weight of a phthalocyanine pigment as the nucleating agent.
DE-OS 1 951 632 discloses the use of carboxylicimide-diphthalimide nucleating agents.
Stocker et al., Macromolecules 31:807-814 (1998), reported the epitaxial crystallization of the metastable phase of isotactic polypropylene (βiPP) on two specific nucleating agents: γ-quinacridone and dicycloterephthalamide.
Varga et al., J. Appl. Poly. Sci. 74:2357-2368 (1999), reported that calcium salts of pimelic and suberic acids are highly active, thermally stable β-nucleating agents and that, in their presence, isotactic homopolymers and random and block copolymers of propylene crystallize almost purely in β modification.
Kotek et al., J. Appl. Poly. Sci. 85:1174-1184, reported the modification of the commercial grade of isotactic polypropylene by N′,N′-dicyclohexyl-naphthalene-2,6-dicarboxamide in a broad concentration range.
Kristiansen et al., Macromolecules 36:5150-5156, investigated the phase behavior of the binary system consisting of the commercial nucleating and clarifying agent 1,3:2,4-bis(3,4-dimethyldibenzylidene)sorbitol and isotactic polypropylene over the entire concentration range by means of differential scanning calorimetry, rheology, and optical microscopy.
Blomenhofer et al., Macromolecules 38:3688-3695, reported the discovery of a family of organic compounds, substituted 1,3,5-benzenetrisamides, that are capable of selectively and efficiently nucleating the growth of the α-crystal modification of isotactic polypropylene, thereby clarifying it, inducing the β-polymorph, or promoting the growth of hybrids of both crystallographic modifications.
See also Polymer Letters 6:539-546 (1968), which discloses a γ-quinacridone nucleating agent.
The disclosures of the foregoing are incorporated herein by reference in their entirety.